Police announced the arrest just hours after they said they had found the remains of a body in the park where they had been searching for the missing woman.

Steven Pieper, 21, of Liverpool, N.Y., was arrested at around 4 p.m. yesterday, and charged with second degree murder.

He pleaded not guilty when he was arraigned that evening in Clay Town Court. Town Justice Brian Lauri ordered Pieper held without bail and he was taken to the Onondaga County Justice Center.

He is due back in court on Friday, Dec. 3.

Watson had decided in October to end her relationship with Pieper, which had been on-again, off-again for 18 months, Onondaga County District Attorney William Fitzpatrick said.

Investigators believe that Pieper, who was a suspect early on in the case, killed Watson at her parents' home shortly before noon on Friday, Nov. 19, then took her to the wooded area near the Clay Town Park, where her body was discovered this morning, Fitzpatrick said.

"We treated Mr. Pieper as far as you folks were concerned as a witness who was cooperating, and yet we knew very, very early on that he was our prime suspect."

The district attorney said there were no visible signs of struggle from Watson.

Earlier yesterday, Fitzpatrick announced that the remains of a body had been found in Clay Central Park, about four miles from Watson's home.

Even before investigators had positively identified the body, Fitzpatrick said the remains were consistent with that of a young, white woman in her 20s.

"Logic and common sense tell us it is likely the remains of Ms. Watson," Fitzpatrick said.

Watson's family has been notified, he said.

For days, Police searched more than 1,200 acres of woods surrounding her family's home in Onondaga County, focusing on the area where her cell phone was last reported active.

"In fact, we tripled the number of personnel that were out here searching because we got involved all of Onondaga County law enforcement," Onondaga County Undersheriff Warren Darby said today on "Good Morning America."

Watson was last seen at home that morning with her parents and 17-year-old sister. When they returned home in the afternoon, Watson was gone, along with her cell phone, though her purse, wallet and house keys were still there.

Neighbors said it was not like the young woman to be out of touch with her family for so long.

"This is out of character for her to be gone for five days is completely out of character," family friend Kelly Kinahan said today on "GMA." "She would communicate with her friends and family on a daily basis. That phone was always glued to her hand."

"She's a ballerina, a wonderful student, keeps in touch with her family, loves her family. It's very out of character for her not to contact anybody," Stacey Kinahan told ABC affiliate WSYR-TV in Syracuse.

Some 600 students attended a vigil Wednesday night at Mercyhurst for the pretty and popular ballet dancer.

"We are all praying for the safe and speedy return of our student to her lovely family," Mercyhurst College president Thomas Gamble said.